University Lowbrow Astronomers

An Observational History of Mars

by Dave Snyder
Printed in Reflections:  April and May 2001
(updated January 2002).

Hubble Space Telescope View of Mars

This year the “Astronomy on the Beach” at Kensington Metropark will focus on Mars and the International Space Station (ISS).  The ISS has generated a lot of interest recently, but why focus on Mars?  I suppose the obvious answer is that Jupiter and Saturn are past their prime for this year and we don’t have any bright comets to work with.  However Mars is a fascinating object and besides, this June Mars will be closer to the earth than it has been at any time since 1988.

Mars has been observed by many ancient cultures - we have no idea who was the first to notice it.  Those who did, noticed a pale pink object that was only visible in the early morning just before dawn (and rather difficult to see at that).  This object moved relative to the stars, got brighter over the next year and rose earlier and earlier.  Then it abruptly stopped and reversed direction.  At its brightest it was the third brightest object in the night sky (only Venus and the Moon were brighter), had an intense red color and was visible all night long.  After moving the “wrong” direction for some 70 days or so, it stopped and reversed direction again.  It gradually got dimmer, was only visible in the evening sky and set earlier and earlier.  After another year it again was a pale pink object, this time only visible just after sunset.  Shortly after that, it could not be seen at all.  It remained hidden for about one hundred days when the cycle repeated again.  Each cycle took a little over two years.

The Greeks named this object Ares after their god of war.  The Romans in turn named it Mars after the roman god of war.

The scientific study of Mars begins in 1600 when various individuals (mainly scientists, but a surprising number of amateurs as well) observed the planet with telescopes.  Our knowledge increased gradually, but certain misconceptions became established, many of which persisted until the last half of the 20th century.  It is then we start to see groups (instead of individuals) studying Mars.  Some of these groups were composed of amateurs, some were composed of scientists and some were composed of both amateurs and scientists.  The most successful of these groups was NASA.  While NASA’s primary objective was landing men on the Moon, clearly the second item on NASA’s priority list was the scientific exploration of Mars using unmanned spacecraft.

NASA, along with its soviet counterpart IKI, sent numerous spacecraft to the red planet.  While there were many failures, there were many successes as well.  In addition, out of the thousands of meteorites that have been examined by scientists, a dozen or so are now known to have originated on Mars.  The data from the spacecraft and the meteorites have dramatically changed our picture of Mars and gave us a seemingly endless set of clues to the geology, chemistry, atmosphere and possible biology of Mars.  However in the process we seemed to have created more questions than answers.

A detailed chronology follows:

The canal controversy would not be completely resolved until spacecraft arrived at Mars.  In the 1960’s most scientists thought there were no canals on Mars, however there were a few exceptions, such as Earl Slipher.  He wrote several books, some of which contained photographs.  Slipher claimed these photographs had lines in the same place as the canals of Percival Lowell.  One of these books was published as late as 1964.  That same year, after a few U. S. and soviet failures, a U. S. spacecraft, Mariner 4, is the first to flyby Mars.  In 1969, Neil Armstrong walks on the Moon.  Some consider that a manned mission to Mars is the next step.  However there are problems with the idea.  A round trip would take two years.  Enough fuel and water must be carried on board so the astronauts could survive and return to earth.  The weight of that fuel and water adds to the expense.  A one way manned trip to Mars (assuming one could find anyone to volunteer for such a thing) seemed manageable, but a round trip seemed too expensive and too difficult.  To date, it has never been attempted, but the idea has been tempting and there are plans to send people to Mars (it remains to be seen if and when these plans will succeed).

Since Mariner 4, the U. S. has sent several spacecraft which either flyby or orbit Mars:  Mariner 6, 7 and 9, Viking 1 and 2, Pathfinder, the Mars Global Surveyor (MGS) and Odyssey.  Odyssey was launched in April 2001 and entered orbit around the red planet in October 2001.  These spacecraft along with several soviet spacecraft have returned thousands of photographs and a vast quantity of other data.  In addition, a dozen or so meteorites are known to have originated on Mars.  Analysis of these meteorites has supplied additional data.

We now have a very different picture of Mars.  Some parts of Mars have numerous craters suggestive of Mercury and the Moon, but other parts of Mars have plains, volcanoes, canyons and river channels.  The volcanoes and canyons are bigger than any other known examples, however there is a vague similarity between some of these features and similar features on the Earth.  There was no evidence of canals or liquid water.  However data prove Mars was warmer and had abundant liquid water in its early history.  Today there is still water, but almost all is in the form of ice in the polar caps and below the surface (some locations on Mars may experience temperatures above the melting point of water, hence transient pools of liquid water are possible).  There is also the possibility Mars may have had tectonic plates like the Earth does now (if so, they were active for only a 500 million years or so).

We now know that the atmosphere has a pressure that varies between 5 and 10 millibars (much lower than anyone had suspected until Mariner 4 made radar occultation measurements).  It is almost entirely carbon dioxide, but contains some water vapor and other trace gases.  The polar caps are partly water ice and partly frozen carbon dioxide, but there are differences between the northern and southern polar caps, as there is between a polar cap seen in the Martian winter and a polar cap seen in the Martian summer.

Since the canals are not real, why were Schiaparelli, Flammarion and Lowell (among others) so convinced they were real?  There are some clues.  First, Schiaparelli was colorblind and this may explain why he saw details others did not.  Once Schiaparelli’s results were known, the power of suggestion may have influenced other observers.  Also, records suggest most observations of canals happened under poor seeing conditions or when small apertures were used.  The canals disappeared under better conditions and larger apertures.  Lowell preferred to reduce the aperture of his scope (which made observing the canals easier), but many of his critics used larger apertures.

There also have been a few tantalizing clues suggestive of life, but to date no proof that Mars has or ever had life.  The most publicized of these clues was a meteorite that was given the designation ALH84001.  ALH84001 is one of the dozen or so meteorites known to come from Mars and had what looked like fossils.  Some scientists believe these fossils come from ancient Martian bacteria, however other scientists are not convinced.  I should note that Viking photographs in the region known as Cydonia look like a human face, but MGS photographs of the same region look like a pile of rocks.  A few non-scientists claim this is a structure built by Martians, however that is unlikely.

There is currently a spacecraft enroute to Mars; it was launched by Japan in 1998.  There were some technical problems, but it is expected to arrive at Mars in late 2003.

Anyone with a telescope can attempt to observe Mars themselves.  The best time to observe Mars is the couple months before and after opposition (the next opposition is in the year 2003).  The rest of the time, it is difficult to see any detail.  Every 15 years there is an exceptionally good opposition; the last one was in 1988, the next one is in 2003.

Observing Mars takes practice.  Details become clear after a little acclimation.  If the seeing is bad, you will not observe as much detail as when the seeing is good so patience is important.  You should try to observe Mars as often as possible during the opposition, this will allow you to track changes in surface and atmospheric features.  When you observe Mars, you may want to try sketching; this will train your eye to observe detail.  Generally the polar caps are the easiest features to see, however you should see the maria and deserts as well.  If you observe over long periods and are patient, you may see clouds, dust storms and various atmospheric phenomena.  You may also notice changes in the polar caps and the maria.

If you have a good telescope and sharp eyes it may be possible to see the two moons, Phobos and Deimos.  At best they have magnitudes 11 and 12, and are rather close to the bright red Mars.

Observers have seen various types of clouds on Mars.  They are known by the labels blue, white, yellow and W-shaped.  These labels can be misleading.  Yellow clouds look yellow to the eye, however blue clouds do not necessarily look blue, white clouds do not necessarily look white and W-shaped clouds are not always W shaped.  Yellow clouds are composed of dust and sometimes grow to cover much of the Martian surface, when this happens it is known as a dust storm.

Having the correct equipment will help your observations.  If you wish to observe surface details, a dark yellow, red and/or orange filter is helpful.  Violet and blue filters are helpful if you want to observe clouds and other atmospheric phenomena (but not yellow clouds or dust storms).  Green filters are helpful for observing the polar caps and other white areas, yellow clouds and dust storms.  If you have made either Jupiter or Saturn observations, you may want eyepieces that provide slightly more magnification than the eyepieces you used for Jupiter and Saturn.

One phenomenon worth mentioning is the violet clearing.  When Mars is observed through a blue or violet filter, it usually appears as a featureless blob (but clouds can sometimes be observed).  However on occasion (usually only once every few years) details on the surface appear.  This lasts a few days; such events are known as violet clearings.  It has been suggested this demonstrates a poorly understood change in the Martian atmosphere, but the best evidence suggests it has nothing to do with the atmosphere at all and is probably an optical illusion.

For more information

The Mars photo above is from the Hubble Space Telescope Wide Field Planetary Camera-2.  It was taken on March 10, 1997, just before opposition and just before summer solstice.  The white area at the top of the photo is the permanent north polar cap.  A haze can be seen in the equatorial region.  The dark area near the center of the photo is Syrtis Major.

See also:

Photo Credits

Credit for the Mars photo: David Crisp and the WFPC2 Science Team (Jet Propulsion Laboratory/California Institute of Technology).


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